In conventional apparatuses for reclaiming foundry sand, the following process has been known to remove dust that is generated when reclaiming the foundry sand: forming a fluidized layer by blowing air into the foundry sand that includes dust; blowing the foundry sand and dust up and into a dust hood for classifying the sand and dust; and classifying them by the differences in the rates at which they settle (for example, Japanese Patent No. 3329757). As a fluidized bed for forming the fluidized layer the structure as in FIG. 6 has been used: That is, slits 101 for upwardly blowing air are formed in a plate with slits 100. If the particles of the sand that have piled around the slits 101 drop through the slits 101 when air stops being blown, they remain on backup plates 102 that are provided under the slits 101. Then when air starts to again be blown they are ejected from the slits 101. together with the air.
However, by the above-mentioned structure of the fluidized bed, the particles of the sand that enter the slits 101 become compressed to thereby form an arch so that clogging 103 is generated in the slits 101. Thus a problem occurs whereby a regular cleaning is required.